Transmission Control Protocol (TCP)/Internet Protocol (IP) is a networking protocol that provides communication across interconnected networks, between computers with diverse hardware architectures and various operating systems. The TCP/IP family of protocols track Internet addresses of nodes, routes outgoing messages and recognizes incoming messages. TCP is a connection-oriented, end-to-end transport layer protocol used to transfer data in a network. IP addresses packets and is the messenger protocol of the TCP/IP family of protocols.
A conventional network interface card (NIC) receives TCP/IP packets from a network and stores the packets in a network interface card memory. A conventional host operating system (OS) copies packets from the network interface card memory to a host memory. A host TCP/IP stack handles TCP/IP protocol processing of the TCP/IP packets. Copying data from the network interface card memory to the host memory may consume a large amount of the host's processing power and is referred to as “overhead.”
The host system may use TCP/IP headers to determine a “connection” associated with each packet. If the TCP/IP packets are received from the network out of order, the host system may use TCP packet sequence numbers in TCP headers to put the TCP/IP packets in a proper order. The host system may also reassemble data (messages) that the network interface card receives in pieces.
As an alternative to the conventional host system, the host system may have a full TCP transport “offload,” where the network interface card does all transport protocol processing instead of the host. This may enable zero copying of received data packets. The network interface card reassembles data packets, replaces out-of-place data packets, identifies the connection to which the packet belongs, and places the data in an appropriate buffer location in host memory. This full transport offload network interface card, however, may be fairly expensive, especially if the network interface card needs to handle a large number of connections and maintain context/connection state information for all connections. The network interface card needs to have high memory bandwidth to access context information to do transport processing. In addition, a host TCP/IP stack needs to be modified to account for the transport offload.
Direct Data Placement (DDP) is a developing protocol described in the “DDP Protocol Specification,” published by an Internet Engineering Task Force (IETF) working group on Oct. 21, 2002 (hereinafter “DDP Specification”). DDP may enable an Upper Layer Protocol (ULP) to send data to a Data Sink without requiring the Data Sink to place the data in an intermediate buffer. When data arrives at the Data Sink, a network interface can place the data directly into the ULP's receive buffer. This may enable the Data Sink to consume substantially less memory bandwidth than a buffered model because the Data Sink is not required to move the data from an intermediate buffer to the final destination. This can also enable the network protocol to consume substantially fewer CPU cycles than if the CPU was used to move data, and remove the bandwidth limitation of being only able to move data as fast as the CPU can copy the data.